Well, my Genesis works fine, but there is one annoying fault. The LED flickers, stays very dim, flickers back to full brightness, and flickers again. I know that LED's typically dont burn out before 20 years of constant usage, so it seems odd. The LED is not a hacked in install, it is a factory default component.
Edit: It only flickers when playing a Genesis game. When playing a Sega CD game it seems to stay at full brightness.